In a wireless communication device such as an ultra-compact microwave wireless communication system, non-reciprocal circuit elements such as a circulator and an isolator are used in order to prevent contamination of a signal and load change in a power amplifier. A non-reciprocal circuit element is generally composed of a ferromagnetic material such as ferrite, a conductor (conductor cover) that applies a high-frequency magnetic field to the ferromagnetic material, a magnet that applies a direct-current field to a conductor and the like. The types of a non-reciprocal circuit element include a waveguide type where a ferromagnetic material is placed inside a waveguide and an SMT (Surface Mount Technology) type where the ferromagnetic material is placed on a transmission line formed on a dielectric substrate. As for the SMT non-reciprocal circuit element, if the same material as a PCB (Printed Circuit Board) is used for a dielectric substrate, the non-reciprocal circuit element can be integrated in the PCB.
The SMT type non-reciprocal circuit element, compared with the waveguide type, can be easily downsized and made with a smaller number of parts, thus enabling easier mounting. On the other hand, the SMT type, compared with the waveguide type, has a problem that the position of a conductor with respect to ferrite is likely to be displaced on a plane parallel to a dielectric substrate surface due to assembly errors at the time of mounting. In order to reduce the displacement of the position of a conductor with respect to ferrite on a plane parallel to a dielectric substrate surface, the SMT non-reciprocal circuit element where the positioning of the side surface (outer surface) of a ferromagnetic material whose lower surface is placed on a transmission line is carried out by the three-point support with protrusions is disclosed, for example, in Patent Literature 1.